flatcontainer/impls/huffman_container.rs
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//! A slice container that Huffman encodes its contents.
use std::collections::BTreeMap;
use crate::{Push, Region};
use self::encoded::Encoded;
use self::huffman::Huffman;
use self::wrapper::Wrapped;
/// A container that contains slices `[B]` as items.
pub struct HuffmanContainer<B: Ord + Clone> {
/// Either encoded data or raw data.
/// Encoded data is a map, a list of bytes, and a number of valid *bits*.
inner: Result<(Huffman<B>, Vec<u8>, usize), Vec<B>>,
/// Counts of the number of each pattern we've seen.
stats: BTreeMap<B, i64>,
}
impl<B> HuffmanContainer<B>
where
B: Ord + Clone,
{
/// Prints statistics about encoded containers.
pub fn print(&self) {
if let Ok((_huff, _bytes, bits)) = &self.inner {
println!(
"Bits: {:?}, Symbols: {:?}",
bits,
self.stats.values().sum::<i64>()
);
}
}
}
impl<B: Ord + Clone> Clone for HuffmanContainer<B> {
fn clone(&self) -> Self {
Self {
inner: self.inner.clone(),
stats: self.stats.clone(),
}
}
fn clone_from(&mut self, source: &Self) {
self.inner.clone_from(&source.inner);
self.stats.clone_from(&source.stats);
}
}
impl<B> Region for HuffmanContainer<B>
where
B: Ord + Clone + Sized + 'static,
{
type Owned = Vec<B>;
type ReadItem<'a> = Wrapped<'a, B>;
type Index = (usize, usize);
fn merge_regions<'a>(regions: impl Iterator<Item = &'a Self> + Clone) -> Self
where
Self: 'a,
{
for region in regions.clone().filter(|r| r.inner.is_ok()) {
region.print();
}
let mut counts = BTreeMap::default();
for (symbol, count) in regions.flat_map(|r| r.stats.iter()) {
*counts.entry(symbol.clone()).or_insert(0) += count;
}
let bytes = Vec::with_capacity(counts.values().cloned().sum::<i64>() as usize);
let huffman = Huffman::create_from(counts);
let inner = Ok((huffman, bytes, 0));
Self {
inner,
stats: Default::default(),
}
}
fn index(&self, (lower, upper): Self::Index) -> Self::ReadItem<'_> {
match &self.inner {
Ok((huffman, bytes, _bits)) => {
Wrapped::encoded(Encoded::new(huffman, bytes, (lower, upper)))
}
Err(raw) => Wrapped::decoded(&raw[lower..upper]),
}
}
fn reserve_regions<'a, I>(&mut self, _regions: I)
where
Self: 'a,
I: Iterator<Item = &'a Self> + Clone,
{
todo!()
}
fn clear(&mut self) {
match &mut self.inner {
Ok(_) => self.inner = Err(Vec::default()),
Err(vec) => vec.clear(),
}
self.stats.clear();
}
fn heap_size<F: FnMut(usize, usize)>(&self, _callback: F) {
todo!()
}
fn reborrow<'b, 'a: 'b>(item: Self::ReadItem<'a>) -> Self::ReadItem<'b>
where
Self: 'a,
{
item
}
}
/// Re-used function to push encoded symbols into a byte vector.
///
/// This function encodes the symbols of `iter` into a sequence of bits,
/// which are bundled as bytes and pushed into `bytes`. The total number
/// of encoded bits is updated at the same time.
///
/// The first three arguments correspond to the `Ok` variant of the
/// `HuffmanContainer` type, and this function would be a method of the
/// hypothetical type that this variant represents.
fn push_symbols<'a, I, B>(
huffman: &'a Huffman<B>,
bytes: &mut Vec<u8>,
bits: &mut usize,
iter: I,
) -> (usize, usize)
where
B: Ord + 'a,
I: Iterator<Item = &'a B>,
{
// We'll only append bits, and start at the number of bits we have already.
let start = *bits;
// Any incomplete bytes are peeled off and re-presented as by the encoder,
// so we should shear them off from the count here to avoid double counting
// when we get encoder outputs.
*bits = *bits - (*bits % 8);
// We may end with a partial byte, in which case we should
// determine and start with those bits, to write the newly
// encoded bits into the same byte.
let initially = if start % 8 == 0 {
(0, 0)
} else {
let bits = start % 8;
let byte = bytes.pop().unwrap() >> (8 - bits);
(byte, bits)
};
// Each encoded by should be pushed, and the number of bits maintained.
// The `Ok` and `Err` variants describe whole and partial bytes, respectively.
for byte in huffman.encode(initially, iter) {
match byte {
Ok(byte) => {
bytes.push(byte);
*bits += 8;
}
Err((byte, bs)) => {
bytes.push(byte);
*bits += bs;
}
}
}
(start, *bits)
}
impl<B> Push<&[B]> for HuffmanContainer<B>
where
B: Ord + Clone + Sized + 'static,
{
fn push(&mut self, item: &[B]) -> (usize, usize) {
for x in item.iter() {
*self.stats.entry(x.clone()).or_insert(0) += 1;
}
match &mut self.inner {
Ok((huffman, bytes, bits)) => push_symbols(huffman, bytes, bits, item.iter()),
Err(raw) => {
let start = raw.len();
raw.extend_from_slice(item);
(start, raw.len())
}
}
}
}
impl<B, const N: usize> Push<[B; N]> for HuffmanContainer<B>
where
B: Ord + Clone + Sized + 'static,
{
fn push(&mut self, item: [B; N]) -> (usize, usize) {
self.push(item.as_slice())
}
}
impl<B, const N: usize> Push<&[B; N]> for HuffmanContainer<B>
where
B: Ord + Clone + Sized + 'static,
{
fn push(&mut self, item: &[B; N]) -> (usize, usize) {
self.push(item.as_slice())
}
}
impl<B> Push<Vec<B>> for HuffmanContainer<B>
where
B: Ord + Clone + Sized + 'static,
{
fn push(&mut self, item: Vec<B>) -> (usize, usize) {
self.push(item.as_slice())
}
}
impl<B> Push<&Vec<B>> for HuffmanContainer<B>
where
B: Ord + Clone + Sized + 'static,
{
fn push(&mut self, item: &Vec<B>) -> (usize, usize) {
self.push(item.as_slice())
}
}
impl<'a, B> Push<Wrapped<'a, B>> for HuffmanContainer<B>
where
B: Ord + Clone + Sized + 'static,
{
fn push(&mut self, item: Wrapped<'a, B>) -> (usize, usize) {
match item.decode() {
Ok(decoded) => {
for x in decoded {
*self.stats.entry(x.clone()).or_insert(0) += 1;
}
}
Err(symbols) => {
for x in symbols.iter() {
*self.stats.entry(x.clone()).or_insert(0) += 1;
}
}
}
match (item.decode(), &mut self.inner) {
(Ok(decoded), Ok((huffman, bytes, bits))) => {
push_symbols(huffman, bytes, bits, decoded)
}
(Ok(decoded), Err(raw)) => {
let start = raw.len();
raw.extend(decoded.cloned());
(start, raw.len())
}
(Err(symbols), Ok((huffman, bytes, bits))) => {
push_symbols(huffman, bytes, bits, symbols.iter())
}
(Err(symbols), Err(raw)) => {
let start = raw.len();
raw.extend(symbols.iter().cloned());
(start, raw.len())
}
}
}
}
impl<B: Ord + Clone> Default for HuffmanContainer<B> {
fn default() -> Self {
Self {
inner: Err(Vec::new()),
stats: Default::default(),
}
}
}
mod wrapper {
use std::fmt::Debug;
use super::Encoded;
pub struct Wrapped<'a, B: Ord> {
inner: Result<Encoded<'a, B>, &'a [B]>,
}
impl<B: Ord + Debug> std::fmt::Debug for Wrapped<'_, B> {
fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> Result<(), std::fmt::Error> {
let mut list = fmt.debug_list();
match &self.inner {
Ok(encoded) => list.entries(encoded.decode()).finish(),
Err(symbols) => list.entries(*symbols).finish(),
}
}
}
impl<'a, B: Ord> Wrapped<'a, B> {
/// Returns either a decoding iterator, or just the bytes themselves.
pub fn decode(&'a self) -> Result<impl Iterator<Item = &'a B> + 'a, &'a [B]> {
match &self.inner {
Ok(encoded) => Ok(encoded.decode()),
Err(symbols) => Err(symbols),
}
}
/// A wrapper around an encoded sequence.
pub fn encoded(e: Encoded<'a, B>) -> Self {
Self { inner: Ok(e) }
}
/// A wrapper around a decoded sequence.
pub fn decoded(d: &'a [B]) -> Self {
Self { inner: Err(d) }
}
}
impl<'a, B: Ord> Copy for Wrapped<'a, B> {}
impl<'a, B: Ord> Clone for Wrapped<'a, B> {
fn clone(&self) -> Self {
*self
}
}
use crate::IntoOwned;
use std::cmp::Ordering;
impl<'a, 'b, B: Ord> PartialEq<Wrapped<'a, B>> for Wrapped<'b, B> {
fn eq(&self, other: &Wrapped<'a, B>) -> bool {
match (self.decode(), other.decode()) {
(Ok(decode1), Ok(decode2)) => decode1.eq(decode2),
(Ok(decode1), Err(bytes2)) => decode1.eq(bytes2.iter()),
(Err(bytes1), Ok(decode2)) => bytes1.iter().eq(decode2),
(Err(bytes1), Err(bytes2)) => bytes1.eq(bytes2),
}
}
}
impl<'a, B: Ord> Eq for Wrapped<'a, B> {}
impl<'a, 'b, B: Ord> PartialOrd<Wrapped<'a, B>> for Wrapped<'b, B> {
fn partial_cmp(&self, other: &Wrapped<'a, B>) -> Option<Ordering> {
match (self.decode(), other.decode()) {
(Ok(decode1), Ok(decode2)) => decode1.partial_cmp(decode2),
(Ok(decode1), Err(bytes2)) => decode1.partial_cmp(bytes2.iter()),
(Err(bytes1), Ok(decode2)) => bytes1.iter().partial_cmp(decode2),
(Err(bytes1), Err(bytes2)) => bytes1.partial_cmp(bytes2),
}
}
}
impl<'a, B: Ord> Ord for Wrapped<'a, B> {
fn cmp(&self, other: &Self) -> Ordering {
self.partial_cmp(other).unwrap()
}
}
impl<'a, B: Ord + Clone> IntoOwned<'a> for Wrapped<'a, B> {
type Owned = Vec<B>;
fn into_owned(self) -> Self::Owned {
match self.decode() {
Ok(iter) => iter.cloned().collect(),
Err(slice) => slice.to_vec(),
}
}
fn clone_onto(self, other: &mut Self::Owned) {
match self.decode() {
Ok(iter) => {
other.clear();
other.extend(iter.cloned());
}
Err(slice) => {
other.clear();
other.extend_from_slice(slice);
}
}
}
fn borrow_as(owned: &'a Self::Owned) -> Self {
Self {
inner: Err(owned.as_slice()),
}
}
}
}
/// Wrapper around a Huffman decoder and byte slices, decodeable to a byte sequence.
mod encoded {
use super::Huffman;
/// Welcome to GATs!
pub struct Encoded<'a, B: Ord> {
/// Text that decorates the data.
huffman: &'a Huffman<B>,
/// The data itself.
bytes: &'a [u8],
/// Bit addressed range, start and end, of valid bits.
///
/// This has the potential to include a partial byte at the start, at the end,
/// and potentially be less than a byte in total for that matter.
bit_range: (usize, usize),
}
impl<'a, B: Ord> Encoded<'a, B> {
/// Returns either a decoding iterator, or just the bytes themselves.
pub fn decode(&'a self) -> impl Iterator<Item = &'a B> + 'a {
let iter = BitIterator {
bytes: self.bytes,
bit_range: self.bit_range,
};
self.huffman.decode(iter)
}
pub fn new(huffman: &'a Huffman<B>, bytes: &'a [u8], bit_range: (usize, usize)) -> Self {
Self {
huffman,
bytes,
bit_range,
}
}
}
impl<'a, B: Ord> Copy for Encoded<'a, B> {}
impl<'a, B: Ord> Clone for Encoded<'a, B> {
fn clone(&self) -> Self {
*self
}
}
/// An iterator over bits in a byte slice.
///
/// The iterator returns a byte at a time and the number of bits in that byte.
/// This can often be a whole valid byte at a time, but the first and last bytes
/// may only contain partial information.
struct BitIterator<'a> {
/// Byte storage within which the addressed bits live.
bytes: &'a [u8],
/// Bit addressed range, start and end, of valid bits.
///
/// This has the potential to include a partial byte at the start, at the end,
/// and potentially be less than a byte in total for that matter.
bit_range: (usize, usize),
}
impl<'a> Iterator for BitIterator<'a> {
type Item = (u8, usize);
fn next(&mut self) -> Option<Self::Item> {
// If bits remain to consume ...
if self.bit_range.0 < self.bit_range.1 {
// We will certainly pull the byte from `self.bytes[self.bit_range.0 / 8]`.
let byte = self.bytes[self.bit_range.0 / 8];
// The number of bits we will pull depends on the start and end of the range.
// We can't pull more bits than our range allows, nor more bits than are in the byte.
let bits = std::cmp::min(
self.bit_range.1 - self.bit_range.0,
8 - self.bit_range.0 % 8,
);
// Now we need to clean up the byte, shifting and masking it.
// This shift depends on the start of the range and the valid bits.
let byte = (byte >> (8 - self.bit_range.0 % 8 - bits)) & ((1 << bits) - 1);
// Advance our cursor to reflect the bits we have consumed.
self.bit_range.0 += bits;
Some((byte, bits))
} else {
None
}
}
}
}
mod huffman {
use std::collections::BTreeMap;
use std::convert::TryInto;
use self::decoder::Decoder;
use self::encoder::Encoder;
/// Encoding and decoding state for Huffman codes.
pub struct Huffman<T: Ord> {
/// byte indexed description of what to blat down for encoding.
/// An entry `(bits, code)` indicates that the low `bits` of `code` should be blatted down.
/// Probably every `code` fits in a `u64`, unless there are crazy frequencies?
encode: BTreeMap<T, (usize, u64)>,
/// Byte-by-byte decoder.
decode: [Decode<T>; 256],
}
impl<T: Ord + Clone> Clone for Huffman<T> {
fn clone(&self) -> Self {
Self {
encode: self.encode.clone(),
decode: self.decode.clone(),
}
}
fn clone_from(&mut self, source: &Self) {
self.encode.clone_from(&source.encode);
self.decode.clone_from(&source.decode);
}
}
impl<T: Ord> Huffman<T> {
/// Encodes the provided symbols as a sequence of bytes.
///
/// The last byte may only contain partial information, but it should be recorded as presented,
/// as we haven't a way to distinguish (e.g. a `Result` return type).
pub fn encode<'a, I>(
&'a self,
initially: (u8, usize),
symbols: I,
) -> Encoder<'a, T, I::IntoIter>
where
I: IntoIterator<Item = &'a T>,
{
Encoder::new(&self.encode, initially, symbols.into_iter())
}
/// Decodes the provided bytes as a sequence of symbols.
pub fn decode<I>(&self, bytes: I) -> Decoder<'_, T, I::IntoIter>
where
I: IntoIterator<Item = (u8, usize)>,
{
Decoder::new(&self.decode, bytes.into_iter())
}
pub fn create_from(counts: BTreeMap<T, i64>) -> Self
where
T: Clone,
{
if counts.is_empty() {
return Self {
encode: Default::default(),
decode: Decode::map(),
};
}
let mut heap = std::collections::BinaryHeap::new();
for (item, count) in counts {
heap.push((-count, Node::Leaf(item)));
}
let mut tree = Vec::with_capacity(2 * heap.len() - 1);
while heap.len() > 1 {
let (count1, least1) = heap.pop().unwrap();
let (count2, least2) = heap.pop().unwrap();
let fork = Node::Fork(tree.len(), tree.len() + 1);
tree.push(least1);
tree.push(least2);
heap.push((count1 + count2, fork));
}
tree.push(heap.pop().unwrap().1);
let mut levels = Vec::with_capacity(1 + tree.len() / 2);
let mut todo = vec![(tree.last().unwrap(), 0)];
while let Some((node, level)) = todo.pop() {
match node {
Node::Leaf(sym) => {
levels.push((level, sym));
}
Node::Fork(l, r) => {
todo.push((&tree[*l], level + 1));
todo.push((&tree[*r], level + 1));
}
}
}
levels.sort_by(|x, y| x.0.cmp(&y.0));
let mut code: u64 = 0;
let mut prev_level = 0;
let mut encode = BTreeMap::new();
let mut decode = Decode::map();
for (level, sym) in levels {
if prev_level != level {
code <<= level - prev_level;
prev_level = level;
}
encode.insert(sym.clone(), (level, code));
Self::insert_decode(&mut decode, sym, level, code << (64 - level));
code += 1;
}
for (index, entry) in decode.iter().enumerate() {
if entry.any_void() {
panic!("VOID FOUND: {:?}", index);
}
}
Huffman { encode, decode }
}
/// Inserts a symbol, and
fn insert_decode(map: &mut [Decode<T>; 256], symbol: &T, bits: usize, code: u64)
where
T: Clone,
{
let byte: u8 = (code >> 56).try_into().unwrap();
if bits <= 8 {
for off in 0..(1 << (8 - bits)) {
map[(byte as usize) + off] = Decode::Symbol(symbol.clone(), bits);
}
} else {
if let Decode::Void = &map[byte as usize] {
map[byte as usize] = Decode::Further(Box::new(Decode::map()));
}
if let Decode::Further(next_map) = &mut map[byte as usize] {
Self::insert_decode(next_map, symbol, bits - 8, code << 8);
}
}
}
}
/// Tree structure for Huffman bit length determination.
#[derive(Eq, PartialEq, Ord, PartialOrd, Debug)]
enum Node<T> {
Leaf(T),
Fork(usize, usize),
}
/// Decoder
#[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Default, Clone)]
pub enum Decode<T> {
/// An as-yet unfilled slot.
#[default]
Void,
/// The symbol, and the number of bits consumed.
Symbol(T, usize),
/// An additional map to push subsequent bytes at.
Further(Box<[Decode<T>; 256]>),
}
impl<T> Decode<T> {
/// Tests to see if the map contains any invalid values.
///
/// A correctly initialized map will have no invalid values.
/// A map with invalid values will be unable to decode some
/// input byte sequences.
fn any_void(&self) -> bool {
match self {
Decode::Void => true,
Decode::Symbol(_, _) => false,
Decode::Further(map) => map.iter().any(|m| m.any_void()),
}
}
/// Creates a new map containing invalid values.
fn map() -> [Decode<T>; 256] {
let mut vec = Vec::with_capacity(256);
for _ in 0..256 {
vec.push(Decode::Void);
}
vec.try_into().ok().unwrap()
}
}
/// A tabled Huffman decoder, written as an iterator.
mod decoder {
use super::Decode;
#[derive(Copy, Clone)]
pub struct Decoder<'a, T, I> {
decode: &'a [Decode<T>; 256],
bytes: I,
pending_byte: u16,
pending_bits: usize,
}
impl<'a, T, I> Decoder<'a, T, I>
where
I: Iterator<Item = (u8, usize)>,
{
pub fn new(decode: &'a [Decode<T>; 256], mut bytes: I) -> Self {
// Read an initial potentially partial byte to start the process.
let (pending_byte, pending_bits) = bytes.next().unwrap_or((0, 0));
Self {
decode,
bytes,
pending_byte: pending_byte.into(),
pending_bits,
}
}
}
impl<'a, T, I> Iterator for Decoder<'a, T, I>
where
I: Iterator<Item = (u8, usize)>,
{
type Item = &'a T;
fn next(&mut self) -> Option<&'a T> {
// We must navigate `self.decode`, restocking bits whenever possible.
// We stop if ever there are not enough bits remaining.
let mut map = self.decode;
loop {
if self.pending_bits < 8 {
// We only attempt to read from `self.bytes` once, which should work fine as long
// as we only have one partial byte at the end, as we are done anyhow in that case.
// It means that we *must* read the initial byte when constructing the iterator, to
// avoid a partial byte in the first read.
if let Some((next_byte, next_bits)) = self.bytes.next() {
self.pending_byte = (self.pending_byte << next_bits) + next_byte as u16;
self.pending_bits += next_bits;
}
}
if self.pending_bits < 8 {
// We have run out of bytes. We may yet be able to decode the remaining bits.
// Promote the valid bits and consult the map; if it only consumes valid bits,
// we are able to ship the result and advance. If it consumes more bits than
// we have, the data are mysteriously invalid.
let byte = (self.pending_byte << (8 - self.pending_bits)) as usize;
match &map[byte] {
Decode::Void => {
panic!("invalid decoding map");
}
Decode::Further(_) => {
panic!("malformed data: decode incomplete (Further)");
}
Decode::Symbol(s, bits) => {
if bits <= &self.pending_bits {
self.pending_bits -= bits;
self.pending_byte &= (1 << self.pending_bits) - 1;
return Some(s);
} else if self.pending_bits == 0 {
return None;
} else {
panic!("malformed data: decode incomplete (Symbol)");
}
}
}
}
let byte = (self.pending_byte >> (self.pending_bits - 8)) as usize;
match &map[byte] {
Decode::Void => {
panic!("invalid decoding map");
}
Decode::Symbol(s, bits) => {
self.pending_bits -= bits;
self.pending_byte &= (1 << self.pending_bits) - 1;
return Some(s);
}
Decode::Further(next_map) => {
self.pending_bits -= 8;
self.pending_byte &= (1 << self.pending_bits) - 1;
map = next_map;
}
}
}
}
}
}
/// A tabled Huffman encoder, written as an iterator.
mod encoder {
use std::collections::BTreeMap;
#[derive(Copy, Clone)]
pub struct Encoder<'a, T, I> {
encode: &'a BTreeMap<T, (usize, u64)>,
symbols: I,
pending_byte: u64,
pending_bits: usize,
}
impl<'a, T, I> Encoder<'a, T, I> {
pub fn new(
encode: &'a BTreeMap<T, (usize, u64)>,
initially: (u8, usize),
symbols: I,
) -> Self {
Self {
encode,
symbols,
pending_byte: initially.0 as u64,
pending_bits: initially.1,
}
}
}
impl<'a, T: Ord, I> Iterator for Encoder<'a, T, I>
where
I: Iterator<Item = &'a T>,
{
type Item = Result<u8, (u8, usize)>;
fn next(&mut self) -> Option<Result<u8, (u8, usize)>> {
// We repeatedly ship bytes out of `self.pending_byte`, restocking from `self.symbols`.
while self.pending_bits < 8 {
if let Some(symbol) = self.symbols.next() {
let (bits, code) = self.encode.get(symbol).unwrap();
self.pending_byte <<= bits;
self.pending_byte += code;
self.pending_bits += bits;
} else {
// We have run out of symbols. Perhaps there is a final fractional byte to ship?
if self.pending_bits > 0 {
let bits = self.pending_bits;
let byte = self.pending_byte << (8 - self.pending_bits);
self.pending_bits = 0;
self.pending_byte = 0;
return Some(Err((byte as u8, bits)));
} else {
return None;
}
}
}
let byte = self.pending_byte >> (self.pending_bits - 8);
self.pending_bits -= 8;
self.pending_byte &= (1 << self.pending_bits) - 1;
Some(Ok(byte as u8))
}
}
}
}
#[cfg(test)]
mod tests {
use crate::{IntoOwned, Push, Region};
use super::*;
#[test]
fn test_huffman() {
let copy = |r: &mut HuffmanContainer<u8>, item: [u8; 3]| {
let index = r.push(item);
println!("{:?}", r.index(index));
assert_eq!(item.as_slice(), r.index(index).into_owned().as_slice());
};
let mut c = HuffmanContainer::<u8>::default();
copy(&mut c, [1, 2, 3]);
copy(&mut c, [1, 2, 3]);
copy(&mut c, [1, 2, 3]);
copy(&mut c, [1, 2, 3]);
copy(&mut c, [2, 3, 4]);
copy(&mut c, [2, 3, 4]);
let mut c2 = HuffmanContainer::merge_regions([&c].into_iter());
copy(&mut c2, [1, 2, 3]);
copy(&mut c2, [1, 2, 3]);
copy(&mut c2, [1, 2, 3]);
copy(&mut c2, [1, 2, 3]);
copy(&mut c2, [2, 3, 4]);
copy(&mut c2, [2, 3, 4]);
let mut c3 = HuffmanContainer::merge_regions([&c2].into_iter());
copy(&mut c3, [1, 2, 3]);
copy(&mut c3, [1, 2, 3]);
copy(&mut c3, [1, 2, 3]);
copy(&mut c3, [1, 2, 3]);
copy(&mut c3, [2, 3, 4]);
copy(&mut c3, [2, 3, 4]);
}
}